未按下按钮时 LED 闪烁，按下按钮时 LED 持续亮起 (Python)

Question

所以，我有一个由 Raspy 控制的 LED，还有一个只有一个按钮的基本 GUI，我希望它的行为如下：

未按下按钮时 LED 闪烁。
当按下按钮时，LED 应持续亮起。

当我执行时，指示灯开始闪烁，但按钮没有显示。 当我中断程序时，按钮出现。为什么？

from tkinter import *
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(8, GPIO.OUT)
GPIO.output(8, False)
buttonPressed = False

master = Tk()

def callback():
    GPIO.output(8, True)
    buttonPressed = True

w = Button(master, text="Turn on light", command = callback)
w.pack()

while True:
    if buttonPressed == False:
        GPIO.output(8, True)
        time.sleep(0.5)
        GPIO.output(8, False)
        time.sleep(0.5)
    else:
        GPIO.output(8, True)

Answer 1

我无法在 RPi 上测试它，但我可以像这样。

普通command=只能在点击按钮时识别，松开按钮时无法识别 - 需要绑定事件<ButtonPress>和<ButtonRelease>，这将运行在 "mouse left button press" 和 "mouse left button release"

上运行

我使用 after() 到运行功能延迟所以我不需要 sleep() 和 while 可以阻止 mainloop() （它可以冻结所有 GUI）。

我也不需要 while 循环因为我运行都在 on_press 和 on_release 以及后来的 after() 运行 s turn_off_led 使用 after() 到运行 turn_on_led 再次使用 after() 到运行 turn_off_led 所以它像循环一样工作。

import tkinter as tk  # PEP8: `import *` is not preferred
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)
GPIO.setup(8, GPIO.OUT)
GPIO.output(8, False)

button_pressed = False  # PEP8: preferred `lower_case_names`

# --- functions ---

def on_press(event):
    global button_pressed

    button_pressed = True
    GPIO.output(8, True)

def on_release(event):
    global button_pressed

    button_pressed = False
    GPIO.output(8, True)

    # run after 500ms (0.5s) instead of `sleep`
    master.after(500, blink_off)

def blink_off():
    if not button_pressed:
        GPIO.output(8, False)
        # run after 500ms (0.5s) instead of `sleep`
        master.after(500, blink_on)

def blink_on():
    if not button_pressed:
        GPIO.output(8, True)
        # run after 500ms (0.5s) instead of `sleep`
        master.after(500, blink_off)

# --- main ---

master = tk.Tk()

button = tk.Button(master, text="Turn on light")
button.pack()

# here "button" means "tk.Button" and "Button" means "mouse left button"
button.bind('<ButtonPress>',   on_press)   # mouse left button pressed on tk.Button 
button.bind('<ButtonRelease>', on_release) # mouse left button released on tk.Button

# start blinking - it will use `after()` to loop
blink_on()

master.mainloop()

Answer 2

我认为@furas 已经为您设定了正确的方向，但由于我是为了好玩而研究它，所以我想我也会把我的解决方案留在这里。我提取了 GPIO 代码，以便我可以在本地运行它。

这两种解决方案的一个关键特征是我们删除了对 time.sleep 的调用，因为当您 time.sleeping 时，Tk 的事件循环无法处理任何事件（这将表现为 UI 在那些睡眠语句中出现在 "freeze" 中）。

import time
import tkinter

buttonpressed = False
lastchange = 0
ledstate = False

def button_down(event):
    global buttonpressed
    print('BUTTON DOWN')
    buttonpressed = True


def button_up(event):
    global buttonpressed
    print('BUTTON UP')
    buttonpressed = False


def myloop(master):
    global buttonpressed
    global lastchange
    global ledstate

    now = time.time()
    delta = now - lastchange

    if not buttonpressed:
        if now - lastchange > 0.5:
            ledstate = not ledstate
            print('LED', ledstate)
            lastchange = now
    else:
        if not ledstate:
            ledstate = True
            print('LED', ledstate)

    master.after_idle(myloop, master)


master = tkinter.Tk()
w = tkinter.Button(master, text="Turn on light")
w.bind('<ButtonPress>', button_down)
w.bind('<ButtonRelease>', button_up)
w.pack()

master.after(100, myloop, master)
master.mainloop()

Answer 3

一个tkinter应用程序需要调用.mainloop()。

你还应该使用 .after(...) 函数来模拟 while 循环:

import tkinter as tk
import RPi.GPIO as GPIO

def led_on(state):
    global button_pressed
    button_pressed = state

def blink_led(state=True):
    # turn on LED if either state or button_pressed is True
    GPIO.output(8, state or button_pressed)
    master.after(500, blink_led, not state) # toggle the state half a second later

# setup the RPi board
GPIO.setmode(GPIO.BOARD)
GPIO.setup(8, GPIO.OUT)
GPIO.output(8, False)

button_pressed = False

master = tk.Tk()

w = tk.Button(master, text='Turn on light')
w.pack()

w.bind('<ButtonPress-1>', lambda e: led_on(True))  # set button_pressed to True
w.bind('<ButtonRelease-1>', lambda e: led_on(False)) # set button_pressed to False

blink_led()  # start the LED blinking

master.mainloop()

未按下按钮时 LED 闪烁，按下按钮时 LED 持续亮起 (Python)

LED to blink when a push button is NOT pressed and to be continually on when the button IS pressed (Python)

python

tkinter

button

light